It is known for quite a while in photographic art to incorporate in silver halide emulsion layers compounds that image-wise release a so-called photographic useful group (PUG) usually as the consequence of a chemical reaction occuring during development. For example, in conventional colour photography use has been made of so-called DIR couplers (Development Inhibitor Releasing), DAR couplers (Development Accelerator Releasing), BIR- and BAR couplers (Bleach Inhibitor- or Accelerator Releasing respectively). During development the PUG is released due to the reaction of the coupler with the p.-phenylenediamine developing agent.
Also PUG carrying developing agents are known such as the inhibitor releasing developers disclosed in e.g. GB 1,058,606 and U.S. Pat. No. 3,841,877. Such compounds are preferably used in combination with free hydroquinone and serve to improve the sharpness characteristics. Hydroquinone and catechol derivatives that release a PUG by means of a conjugated addition-elimination mechanism due to an intramolecular nucleophilic group attack are disclosed in U.S. Pat. No. 5,202,225.
When the PUG is a dye or a dye precursor, for instance a p.-phenylenediamine moiety, the compound can be used in special colour forming systems. An example of such a PUG releasing system, based on an intramolecular nucleophilic displacement reaction is disclosed in EP 0 295 729.
Still other PUG releasing systems, especially suited for graphic arts materials, are disclosed wherein the PUG is attached to a basic hydrazine or hydrazide structure or where the PUG releasing compound is used in combination with a conventional hydrazinc or hydrazide. Examples of disclosures on these latter types can be found in e.g. U.S. Pat. Nos. 4,737,442, 4,684,604, EP 0 393 720, EP 0 393 721, EP 0 395 069, U.S. Pat. No. 5,278,025, EP 0 306 833, EP 0 399 460, U.S. Pat. Nos. 5,006,444, 5,258,259, EP 0 420 005, U.S. Pat. Nos. 5,155,006, 5,124,231, EP 0 452 848, U.S. Pat. Nos. 5,252,438, 5,262,274, 5,328,801, 5,286,598, and in the Unexamined Japanese Patent Applications (Kokai) Nos. 63-271347, 63-296032, 01-088451, 01-072140, 01-072144, 02-275439, 02-285340, 02-287532, 02-293736, 02-304433, 03-100543, 03-100646, 03-119348, 03-067241, 03-067242, 03-067244, 03-067245, 03-067246, 03-137633, 03-150554, 04-119349, 04-163446, 04-313749, 04-316038, 04-321023, 05-045767, 05-088290, 05-313276.
The present invention extends the teachings on PUG releasing compounds in photographic materials.
It is the object of the present invention to provide a new type of PUG releasing compounds, and their application in photographic materials, which release their PUG in a very effective way and according to a new mechanism.